1. Field of the Invention
The present invention relates to a connection control system and a method in a switch.
2. Description of the Related Art
Discussions about an ATM (Asynchronous Transfer Mode) switching technique are frequently made as a technique for implementing a broadband ISDN (Integrated Services Digital Network) of a next-generation switching system, in various organizations. An ATM switch exchanges contents of subscriber information (data, voice data, image data, etc.) using a fixed-length packet called a cell. The ATM switch identifies each connection according to a value of a VPI/VCI defined in a header of the cell, and makes the cell self-route to a target output line by adding routing information called a tag corresponding to a connection specified in the input cell at an entry point of the switch. This capability is one of the features of the ATM switching method.
A connection is normally a pair of an upward connection (from a subscriber at a source side to a subscriber at a destination side) and a downward connection (from the subscriber at the destination side to the subscriber at the source side). Therefore, if a connection is established between these two subscribers, an instruction for establishing the connection must be given to line response units at both sides where the subscribers are respectively accommodated. Accordingly, a timing when the subscriber information can be transferred in the upward connection is different from that in the downward connection, and a time for establishing the connection is expected to be longer. Therefore, it is vital to shorten the time for establishing the connection.
In a conventional switching control method, as shown in FIG. 1, a central control processor (CC) 101 which controls a call outputs an instruction for establishing a connection corresponding to each of microprocessors (.mu.ps) in each of line response units 103 at source and destination sides, with an ATM switch 102 in between. Each of the microprocessors in each of the line response units 103 sets connection information for each piece of hardware in each of the line response units. Such hardware details a UPC (Usage Parameter Control) unit, an NPC (Network Parameter Control) unit, an accounting counter unit, a VCC (Virtual Channel Controller) table, etc.
With the conventional technique shown in FIG. 1, however, when a CC 101 transmits the instruction of establishing a connection to each of the line response units 103 at the source and destination sides, a process delay until an establishment of the connection becomes extended.
If a result of the process of establishing a connection in either of the line response units 103 is NG, an instruction for releasing the connection must be given to the other of the line response units 103 in which the result of the process of establishing the connection is OK. As a result, control of establishing a connection becomes complicated.
Even if the instruction for establishing the connection is transmitted respectively to the line response units 103 at the source and destination sides, it does not verify a proper exchange of cells between the line response units 103 at the source and destination sides via the ATM switch 102. Accordingly, the cells may not flow properly when a subscriber starts a communication.
Furthermore, since the line response units 103 at the source and destination sides work both mutually and independently, it is difficult to examine the quality of the overall connection between the line response units 103 at the source and destination sides.